Although high levels of glucocorticoids are commonly linked to stress and impaired reproduction, there are species which show elevations in these steroids during breeding readiness. In musk shrews interactions between males and females are marked by an initial aggressive phase, followed by a rapid transition to receptivity and copulation. Studies will examine interactions between the adrenal glucocorticoids and reproduction in male and female musk shrews. The primary hypotheses are that adrenal steroids increase during breeding interactions, facilitate display of sexual behavior and modify the neuronal substrates that influence reproductive success. New radio-immunoassays will be developed to measure glucocorticoids over the course of a mating bout. Classic removal and replacement techniques will be used to determine if glucocorticoids facilitate the display of sexual behavior. The distribution of glucocorticoid receptors in the musk shrew brain will be assessed. Double antibody immunocytochemistry will be conducted to locate GnRH containing- cells that may be directly affected by glucocorticoids via glucocorticoid receptors.